In recent years, the trend toward micro-scale pattern rule has been increasing with the trend toward large-scale integration and high-speed of LSI. The trend toward a shorter wavelength of the exposure light source lies behind it. For example, it has become possible to mass-produce DRAM (dynamic random-access memory) of 64M-bit (processing dimension is 0.25 μm or less) by the wavelength shortening from mercury lamp i-line (365 nm) to KrF excimer laser (248 nm). Furthermore, in order to realize the production of DRAM's having integration degrees of 256M and 1 G or greater, a lithography using ArF excimer laser (193 nm) has been studied on a full scale, and a 65 nm node device has been studied by a combination with a high NA lens (NA≧0.9). Although the use of F2 laser having a wavelength of 157 nm had been named as a candidate for the production of the next 45 nm node devices, the application was postponed by many problems represented by cost increase of scanner, change of optical system, low etching resistance of resist, and the like. As an alternative to F2 lithography, proposed was ArF immersion lithography. Now, its introduction is beginning. Furthermore, extreme ultraviolet (EUV) lithography is regarded as being promising in a design rule of 45 nm or less.
As a resist suitable for such exposure wavelength, “chemically amplified resist material” attracts much attention. This contains a radiosensitive acid generator (hereinafter referred to as “photoacid generator”), which generates an acid by radiation irradiation (hereinafter, referred to as “exposure”), and is a pattern-forming material that forms a pattern by making a difference in solubility between the exposed portion and the unexposed portion through a reaction using the acid generated by the exposure as a catalyst.
Various studies have also been conducted with respect to a photoacid generator used for such chemically amplified resist material. In case that a photoacid generator that generates an alkane or arenesulfonic acid, as used for chemically amplified resist materials, for which a conventional KrF excimer laser light is used as the light source, is used as a component of the above ArF chemically amplified resist materials, it is known that acid strength for severing an acid-labile group of the resin is not sufficient, resulting in no possibility of resolution at all, or it is known to be not suitable for device production due to low sensitivity.
Therefore, as a photoacid generator of ArF chemically amplified resist materials, one that generates a perfluoroalkanesulfonic acid, which is high in acid strength, is generally used. Perfluorooctanesulfonic acid, or its derivatives are, however, known as PFOS by its initials, and stability (undegradability) and hydrophobicity resulting from C—F bond, and ecological concentration and accumulation resulting from oleophilicity have become problems. Furthermore, a perfluoroalkanesulfonic acid having a carbon number of 5 or greater or its derivatives are also beginning to pose the above problems.
To deal with problems related to such PFOS, there is conducted by each company the development of a photoacid generator having a structure getting rid of PFOS skeleton, while maintaining level of acidity.
In Patent Publication 1, it is shown that a compound having an imide or methide acid is effective as an initiator, curing agent or catalyst, since it has a solubility in organic solvents and improves catalytic activity. After that, there have been disclosed many examples in which such compound having an imide or methide acid is used as a photoacid generator of chemically amplified resist materials (Patent Publication 2, Patent Publication 3, Patent Publication 4, Patent Publication 5, and Patent Publication 6). Furthermore, there is a report in Patent Publication 7 that a salt having a fluorine-containing carbanion that is analogous to methide anion (a carb anion having a carbon number of 1) acts as a photoacid generator. Furthermore, in Patent Publication 8, there is disclosed a method in which a polymerization is conducted by using a polymerizable cation, a photoacid generator itself is immobilized in a resist resin, and an imide or methide acid is used as the anion.    Patent Publication 1: Japanese Patent Application Publication 11-501909    Patent Publication 2: Japanese Patent Application Publication 2002-268223    Patent Publication 3: Japanese Patent Application Publication 2004-85657    Patent Publication 4: Japanese Patent Application Publication 2005-173464    Patent Publication 5: Japanese Patent Application Publication 2007-86166    Patent Publication 6: Japanese Patent Application Publication 2007-241121    Patent Publication 7: Japanese Patent Application Publication 2007-219411    Patent Publication 1: Japanese Patent Application Publication 2007-316600